The decision-feedback sequence estimator (DFSE) is a very effective approximation to the maximum likelihood sequence estimator (MLSE), which is the optimal equalizer in a certain sense. The DFSE has a much reduced complexity in comparison to the MLSE, while maintaining comparable performance. It has been applied effectively to wireless receivers for the GSM standard, which employs GMSK modulation, as well as to receivers developed for GSM's evolutionary standard, EDGE (Enhanced Data for GSM Evolution), which uses 8PSK modulation.
With the introduction of larger modulation constellations (e.g., 64-QAM) in more recent wireless communication standards, as well as with the increased complexity arising from the deployment of multiple antenna transmission strategies, it is increasingly important to design new equalizers with still further complexity reduction compared to the conventional DFSE, while still maintaining good performance.